Means for segregating currents of different frequencies in electricity-conducting systems.



L. T. MERWIN & R. K. FREEMAN.

MEANS FOR SEGREGATING CURRENTS OF DIFFERENT FREQUENCIES m ELECTRICITY CONDUCTING SYSIEMS.

APPLICATION FILED AUG.3I. 1915.

Patented Nov, 12, 1918.

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LOUIS T. MERWIN AND RQY K. FREEMAN, 0F PORTLAND, OREGON.

MEANS FOR SEGREGATING CURRENTS OF DIFFERENT FREQUENCIES IN ELECTRICITY- CONDUCTING SYSTEMS. I

Specification of Letters Patent.

Patented Nov. 12, 1918.

' Application filed August 81-, 1915. Serial No.- 48,357.

To all whom it may concern:

Be it known that we, Louis T. MERWIN and ROY K. FREEMAN, citizens of the United States, and residents of Portland. county of Multnomah, State of Oregon, have invented a new and useful Improvement in Means for segregating Currents of Diflerent Frequencies in Electricity-Conducting Systems, of which the following is a specification.

This invention relates to means for segregating and conducting along individual paths certain selected frequencies present in the circuit of an alternating or pulsating electrical current.

In electricity conducting systems which carry alternating or pulsating currents, a plurality of frequencies varying in phase and magnitude are carried by the conductors, some of these frequencies being primarily developed in the svstem and others being induced into the system.

Detecting instruments located in the circuit are adapted to respond to certain frequencies and the presence of other interfering frequencies in the'circuit of the instrument tends to reduce the efficiency of the latter.

In a prior patent application filed by us on Feb. 5th, 1915. Ser. No. 6.383. under title Method and means for eliminating disturbing frequencies in electricity conducting systems, we illustrated a type of selective transformer, by the action of which, certain selected frequencies were eliminated from the system.

In the present application, the main object of the invention is not to eliminate these selected frequencies from the circuit but to short-circuit them about the detecting instrument and allow only the frequencies to be used to pass through the instrument.

We attain this object of our invention by making use of the properties of the impedances which .exist in circuits of the character described. The impedance in an alternating or pulsating current is expressed by the following formula, assuming sine waves:

. 2 w l i in which Z equals impedance R ohmic resistance f frequency L inductive reactance C condensive reactance.

It will be observed by an inspection of this formula that the impedance is a function of the frequency, 6- with a given inductance and capacity, the impedance will vary with the frequency. Furthermore, it will be also observed that the impedance does not vary directly as the frequency.

Therefore, assuming that we introduce into a circuit a shunt which contains impedance having a lowvalue for one frequency and having a higher value for all other frequencies, and assuming further the continuation of the main circuit with impedance having a high value for the first mentioned frequency and a lower value for some other frequency, it will be obvious that the circuit will be divided so thatthe first mentioned frequency will flow through the shunt circuit, and all other frequencieswill flow through the continuation of the main circuit. Detecting instruments may .be placed in either .path and will respond to the frequencies flowing through that path.

The use of this principle has many useful adaptations, of which the following examples are typical: In a telephone line, paralleling a power line, induced frequencies of low value pass through the receiver and interfere with the high talking frequencies. In multiplex telegraphy, a plurality of different frequencies may be segregated and conducted along individual paths through detecting instruments adapted to respond to the particular frequencies. In wireless telegraphy, selective signal work, and many other forms of electrical endeavor, this principle may also be used to great advantage.

In the accompanying illustrations, are shown three adaptations of our device, and in these illustrations,

Figure l is a diagrammatic view showing the multiple arrangement of the device for short-circuiting a low frequency or group of low frequencies across the line.

Fig. 2 is a similar view showing the multiple arrangement of the device for shortcircuiting a plurality of selected frequencies across the line, and Fig. 3 is a view showing a series arrangement of the device for short-circuiting a particular frequency around the detectlng instrument.

a and 6 represent the conductors of an alternating or pulsating electricity circuit, and D is a detecting instrument located in the line. I

In Fig. 1, it is assumed that an induced low frequency in the line interferes with the high frequency to be used in the operation of the detecting instrument. Therefore, a short-circuit conductor e is connected to the conductor a at the point A and this conductor is divided into the two branches f and 9. Adjustable condensers C and C are placed in the branches 7 and 9, respectively, and an adjustable inductance L is also placed in the branch 9. The branch conductors f and g are then mutually related by being differentially Wound as indicated by f and 9' around a core of high magnetic permeability preferably closed iron core M, and connected to the conductor 6, at the point B by a conductor It. An adjustable condenser element C is placed in the conductor a, between the detector D and the short-circuit conductor e.

The action of this net-work in short-circuiting the selected low frequency is as follows:

Assuming a plurality of various frequencies to be present in the conductor a, one of which frequencies we will call F, a portion of the current in a, flows through 6 and divides intothe branch conductors f and 9.

Assuming the ohmic resistance to be negligibly small, any arbitrary choice of value for C will give a certain potential drop in the branch f for the frequency F.

The reactance members C and L are next adjusted so that the drop in potential in the branch 9 will be equal to that in the branch f, for said frequency F. If, now, the branches f and g are connected to the conductor 6, equal currents of the frequency F will flow through said branches. For all the other frequencies, however, the impedances will have different values, and consequently the potential drop in the branch f memes If now, the branches 7 and g are ini ductively related so that further impedances are introduced which will have a low value for equal currents and a high value for unequal currents, the branches f and 9 become true short-circuit paths for the frequency F, only, and paths of high impedance for all other frequencies.

So it may be said that the function of the differential winding is to offer a path of low impedance for the currents of a certain frequency in the two branches that have been made equal in phase and magnitude by adjustment of the impedances in those branches, but which offers at the same time a path of higher impedance for currents of all other frequencies.

This inductive relationship between the a two branches may be brought about by providing the differential windings f and g on a closed iron core M so as to assure the least possible magnetic leakage. This means a closed magnetic circuit with a closely overlapped and intermingled pair of windings, and the point H at which the conductor h is connected to the windings is of course to be so chosen that the magnetizing forces impressed on these mutual inductance coils are equal in phase and magnitude for cur rents of the same phase and frequency, but unequal in phase and magnitude for unequal currents.

With said mutual inductance introduced into the branches f and g, these branches become true short-circuit paths of low impedance for frequency F, but paths of high impedance for all other frequencies. Hence, currents of other frequencies will be choked back out of the short-circuit path, and conducted on through the detecting instrument D with very slight leakage, while the frequency F will be short-circuited past the instrument. t

In Fig. 2, the arrangement of the shortcircuited net-work is substantially equivalent to that shown in Fig. 1, the difference being that the latter is arranged to select and short-circuit a plurality of frequencies. For this purpose there are connected in multiple with the conductor 9 the additional paths m and n, in which are contained the condenser and inductance elements C, C, L, and L located respectiveely as shown in this figure.

It has been seen by the description relating to Fig. 1, that the frequency F was short-circuited across the line from A to. B while the other frequencies were conducted past the pointA through the detector D. In

this case, let us assume that two other frequencies F and F are also to be short-cir cuited across the line. Leaving the setting for C, as originally made'the condenser statement, supm, that the impedance 0' may be of, any value, and the impedance C in the branch 9 is adjusted to form a path of lower impedance for 'branch f. And there are" similar adjustments of the values of the impedance in the branches m, n. The imped ances in the branches 9, m, n, are independent of each other, or, in other words, the relation of the branch f to branch 9 does in no wise impair the relation of branch f to branch m, orv to branch n.

The frequency F, will then be short-circuited in a manner similar to frequency F. Similarly a frequency F may be short-circuited through the reactance branch 11., when the latter is used in combination with the branch 7.

And it is now evident that for any setting of C, and usin any number of branches such as g, m, n, t e impedances in these latter branches may be so adjusted as to form short-circuit paths for various frequencies; that is to say, each branch throu h its mutual relation to 0' being adapte to shortcircuit one particular frequency.

It is also apparent that the short-circuit branch may be treated as an original circuit, and sub-short-circuits provided .as desired with detecting instruments placed in such circuits. I

By continuing the arrangement shown in Fig. 2, it is evident that under ideal conditions, any number of frequencies may be short-circuited. I t v In Fig. 3, the arrangement shows the same short-circuit net-work detailed in Fig. 1. In this net-work however, the conductor 7:. is connected to the conductor a, and the short-circuited frequencies are merelyv carried around the detecting instrument D instead of across the line.

In this case, the inductance L is substis tuted for the condenser O in Fig. 1 for the purpose of permitting high frequencies to be short-circuited around the detector D, and low frequencies allowed to pass through the latter. V

We claim: 7

1. In an electricity conducting system of the character described, means for segregat-v mg a certainfrequency comprising a main .circuit provided with a shunt, the latter be-- ing. divided into' branches, impedances in such branches, and differential windings connected with said branches, through which said branches are mutually related.

2. In an electricity conducting system of the-character described, means for segregating a certain frequency comprisin a main circuit provided with a shunt, the Iatter being divided into branches, im edances in such branches, the impedance 0 one branch being adjustable, and differential windings connected with said branches, through which said branches are mutually related.

3. In an electricity conducting system of the character described, means for segregating a certain frequency comprising a main circuit provided with a shunt, the latter being divided into branches, impedances in such branches, and a core having diflerential windings, connected with said branches, through which said branches are mutually related.

, 4. In an electricity conducting system of the character described, means for segregating a certain frequency comprising a main circuit provided with. a shunt, the latter being divided into branches, impedances in such branches, and a core of high permeability having differential windmgs, connected with said branches, throu h which said branches are mutually relate 5. In .an electricity conducting system of the character-described, means for segregating'a certainfrequency comprisin a main circuit provided with a shunt, the atter being divided into branches, im edances in such branches the impedance 0 one branch being adjustable, and a core havin difierential windings, connected wit said branches, through which said branches are LOUIS T. MERWIN? ROY K. FREEMAN.

mutually related.

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